1. Field of the Invention
The invention generally relates to a lens and an optical device. More particularly, the invention relates to a projection lens and an optical engine.
2. Description of Related Art
Generally, in design of large-aperture projection lens, since an aperture thereof is relatively larger, the design usually requires a plurality of lenses to ensure a preferable optical imaging quality. A more preferable structure may only use six pieces of lenses to meet the design requirement. However, the structure must use aspherical lens to reduce aberration.
In addition, in the case where the aspherical lens is used for reducing aberration, if the aspherical lens close to the aperture stop is poorly designed, a sensitivity of the aspherical lens to imaging quality may be significantly increased, such that mass production of the projection lens can not be easily accomplished.
In addition, projector nowadays is designed to have light weight and compact size, so that internal temperature of projector may not be easily reduced. Once the aspherical lens is affected by a higher temperature, a thermal drift effect may occur accordingly, such that a gradually blurred projected image may been seen after the projector being turned on.
U.S. Pat. No. 6,715,889 discloses a projecting lens, a supporting member, a beam-splitting prism and a light modulation device. U.S. Pat. No. 7,612,951 discloses a thermal deformable barrel having a movable lens barrel and a bimetal member. Once temperature is raised, the bimetal member may be deformed by the thermal effect to move lens by moving the movable lens barrel, thereby causing a back focus position of the optical system to move.